Caption: Polarised light micrograph of foraminifera shells. Foraminifera are single celled amoeboid protists. They live within a shell, or test, which can be composed of a single chamber or a number of chambers. Protoplasm extrudes through holes in the shell to facilitate feeding. Most species are marine and the shells are most commonly formed of calcium carbonate. The shells of these tiny creatures formed large deposits of limestone. Magnification: x27 at 10cm wide.